The present invention relates generally to the art of electrical power substrates. More particularly, the invention relates to an advantageous arrangement of switching devices and diodes in an inverting circuit of the type used in power substrates.
In the art of power electronics, numerous applications are known for switch-mode inverter circuits. Such circuits typically include a pair of solid state switching devices, such as semiconductor controlled rectifiers (SCR's), power transistors, insulated gate bipolar transistors (IGBT's) or the like, coupled in series across a direct current (DC) power bus. A flyback diode is coupled in parallel with each switching device. Input DC power is commonly applied to the inverter circuit via a direct current bus from a rectifying and filtering circuit coupled to a source of alternating current (AC) power. By controlled operation of the switching devices, such as by pulse-width-modulation, AC power output is obtained in an output line between the switching devices at desired frequency and voltage. The circuits may be configured for single or three phase applications, such as in AC motor drives.
During controlled switching of such inverter circuits, voltage spikes are commonly encountered due to parasitic inductance, particularly between the switching devices and the output line. In particular, due to the topology of known inverter circuits, parasitic inductance is problematic during transient turnoff periods due to the length of current carrying paths between each switching device and the opposing diode, as well as to the close proximity of the flyback diodes to their corresponding switching devices, and the proximity of current paths between the output line and the diodes. The adverse effects of such parasitic inductance is especially troublesome in applications where controlled switching is extremely rapid, such as in pulse-width-modulation techniques used to generate AC output having desired waveforms.
Thus, there is a need for an improved inverter topology which reduces or eliminates such parasitic inductance and thereby improves the characteristics of the output power waveforms. In particular, there is a need for an improved circuit topology of this type that can be employed in a rather straightforward manner in both single phase and three phase inverter arrangements, such as in power substrates for devices such as variable frequency motor drives.